This invention relates to an articulated aerial device with a plurality of interconnected booms including a lower boom and an upper boom and having a hydraulic upper boom compensation apparatus, and particularly a hydraulically actuated upper boom angle control for maintaining the upper boom angle relative to the lower boom during the raising and lowering of the lower boom assembly.
The compensation of the upper boom is desirable to maintain the angular orientation with respect to the ground or other support structure in a constant relative position. Thus, a supporting basket or other member is often secured to the uppermost boom within which workmen and equipment reside for operating in the aerial position.
An improved articulated aerial device such as widely used for locating operating personnel at elevated levels as well as requiring prompt elevated positioning is disclosed in U.S. Pat. No. 5,819,534, issued Oct. 13, 1998. The lift system disclosed therein includes a hydraulic motor assembly interconnecting the upper and lower boom and a lifting apparatus for pivoting of the lower boom. The hydraulic circuit for the upper boom includes a separate compensating cylinder unit which is connected in end relationship to the upper boom positioning cylinder unit. The compensating cylinder unit is a separate unit secured to the lift cylinder unit including separate interconnections and mounting relative to the upper boom positioning cylinder unit with an interrelated special fluid controlled supply and exit from the separate compensating cylinder. A lower boom hydraulic supply is connected to a control unit to supply hydraulic fluid to the lower boom cylinder unit, and simultaneously to the upper boom compensating cylinder unit to provide a coordinated position control. The system permits the independent positioning of the two booms. Thereafter, the separate compensating cylinder unit is controlled in response to the lowering and raising of the lower boom to establish automatic compensation by redirecting of the pressurized hydraulic fluid to the compensating system including the separate compensation cylinder and the lower boom cylinder to maintain a desired positioning of the upper boom.
Although the system provides a highly effective hydraulic compensating system for movement of the lower boom unit and the upper boom unit, the separate special cylinder construction requires a multiple interconnection and mounting of the apparatus and connecting of the various hydraulic systems.
The present invention is directed to a hydraulic system for controlling the relative position of an upper boom relative to the ground with a single integrated upper boom positioning and compensating cylinder unit (hereinafter referred to as an upper boom/compensating cylinder unit) including a rod end and a base end as a single hydraulic cylinder in combination with separate hydraulic supply unit to the upper boom and connection of the lower positioning unit to the supply with the integrated upper boom/compensating cylinder unit. A separate compensating manifold or module unit is interconnected to the opposite elements of the upper boom/compensating cylinder unit which responds with an interrelated control of the lower boom lifting apparatus. This permits the independent positioning of the lower boom and the upper boom as well as maintaining the desired orientation of the upper boom with changes in the lower boom without changing of the angular orientation of the upper end of the upper boom relative to the base supporting system of the booms.
In accordance with the present invention, the upper boom/compensating cylinder unit is formed as a single cylinder having a rod end inclusive of a piston and a rod projecting outwardly of the positioning rod end. The piston defines a compensating cylinder end extending outwardly in the opposite direction of the piston from the rod end. For independently positioning of the upper boom, a first flow control system is connected to provide differential proportional flow to and from the rod end and the base end of the upper boom/compensating cylinder unit in accordance with the difference in the cross sectional and volumetric capacity of the respective chambers. In addition, a separate module section is interconnected between the rod end and the base end of the cylinder of the upper boom/compensation cylinder and the lower boom hydraulic positioning unit to establish a hydraulic fluid flow to and from the lower boom cylinder unit and with a compensating flow from the upper boom and compensating cylinder unit to maintain a desired precise orientation between the upper boom and the ground.
The present invention establishes a simplified system providing for independent boom positioning as well as the interrelated control.
In the preferred construction, the upper boom control includes a holding valve assembly which may have a direct control for the independent movement of the upper boom unit. The main positioning control of the upper boom produces direct upper boom positioning thereof is through a special supply for balancing the flow to and from the opposite ends of the upper boom cylinder unit as such. It permits controlling of the angle of the upper boom relative to the lower boom. The interconnection of the lower boom hydraulic system includes a holding valve manifold connected to a similar manifold at the upper boom/compensating unit which provides for a necessary hydraulic flow from the supply and to and from the respective rod end and base end of the respective lower and upper boom units for positioning of the lower boom and repositioning of the upper boom.
The present invention thus provides a hydraulic system for providing of a hydraulic upper boom compensation and maintaining the orientation between the upper boom and the ground with a simplified and more cost effective system.